1. Field of the Invention
The present invention relates to a fixing device for fixing developer that has been transferred onto a recording medium. The present invention also relates to an image forming device employing the fixing device.
2. Description of Related Art
An image forming device such as a laser printer is conventionally provided with a fixing device for fixing developer that has been transferred onto a recording medium. A typical fixing device includes a cylindrical heating roller and a pressure roller disposed parallel to and in contact with the heating roller. Developer such as toner that has been transferred onto a recording medium such as paper is fixed onto the recording medium, as the medium passes between the heating roller and the pressure roller, by the heat of the heating roller, which is heated to about 150° C. (degrees Celsius).
Conventional fixing devices employ a halogen lamp or an electromagnetic induction type heating device as a source for heating the heating roller. In the former type of fixing device, a halogen lamp is disposed inside a hollow heating roller. When an electric current flows through the halogen lamp, infrared rays emitted from the halogen lamp strike the inside walls of the heating roller, generating heat that is transferred to the surface of the roller. This construction requires fasteners or fixing mechanisms for fixing the halogen lamp in the heating roller, a component for connecting the halogen lamp to an electric circuit, and the like. Since parts that do not contact the paper, including the fasteners and the connecting component, are all heated uniformly, a large amount of heat is dissipated in the air, wasting much energy. Moreover, a longer warm-up time is required for the heating roller to reach the required temperature for fixing the developer (around 150° C.) after a current is applied to the halogen lamp.
In contrast, fixing devices that employ an electromagnetic induction type heating device to heat the heating roller can decrease the amount of wasted energy and can reduce the warm-up time.
For example, Japanese patent application publication No. HEI-11-297462 discloses a fixing device employing an electromagnetic-induction heating device. The fixing device includes a heating roller with an iron cylinder core and a pressure roller and disposes the electromagnetic-induction heating device on the side of the heating roller opposite the area contacting the recording medium. The electromagnetic-induction type heating device is configured such that a coil is supported along the outer surface of the heating roller by a support. When an alternating current is supplied to the coil, a magnetic-field is generated around the coil and magnetic flux passing through the surface of the heating roller generates an eddy current. Joule heat is generated on the surface of the heating roller by the eddy current and the resistivity on the surface of the heating roller, thereby heating the heating roller.